1. Field of the Invention
The present invention relates to a projection type display using a light valve, particularly to the projection type display using a transmission type liquid crystal light valve.
2. Description of the Related Art
Among projection type displays using a valve for light modulation, a projection type display using a liquid crystal light valve, what is called, a liquid crystal projector can display a fine and large screen and therefore has a possibility to take the place of a display (CRT) for a home television or a personal computer (PC) in near future. Recently, along with an increase in display resolution required for the PC display, more fine and higher resolution for the liquid crystal projector is realized. The resolution proceeds from the conventional 640xc3x97480 dots (VGA) to 800xc3x97600 dots (SVGA) as a standard, and also to more fine 1024xc3x97768 dots (XGA) in future.
A schematic structure of the conventional liquid crystal projector 1 is briefly described with reference to FIG. 15. A projection optical system of the liquid crystal projector 1 comprises a lamp 2, a liquid crystal light valve section 4, and a projection lens 6. Although a diagram is omitted, the projection optical system also comprises a plurality of dichroic mirrors for separating light from the lamp 2 into three colors of red, green and blue, and a dichroic prism (or a plurality of dichroic mirrors) for synthesizing the three separated colors. The separated three colors respectively enter a liquid crystal light valve for each color provided in the liquid crystal light valve section 4, and are modulated according to an image signal, thereby emitting to the projection lens 6 after synthesized at the dichroic prism.
An image signal processing system in the liquid crystal projector 1 comprises a control circuit 8 to which a picture signal from the PC, the video equipment or the like inputs. The picture signal input to the control circuit 8 is converted to a predetermined voltage and supplied to each liquid crystal light valve in the liquid crystal light valve section 4 through a signal line 18. A driving voltage according to the picture signal is applied to each pixel of the liquid crystal light valve, thus allowing to obtain an image on a screen by changing transmissivity of each pixel in response to the picture signal and modulating the light from the lamp 2. Ordinary, a light source capable of producing a large amount of light such as a metal halide lamp and the like is used as the lamp 2. Hence, a large electric power is supplied from a power supply 26 through a power line 24 and the lamp 2 produces heat to a high temperature.
The heat produced at the lamp 2 increases an internal temperature of the liquid crystal projector 1 (body) by radiation or heat conduction through air. Also, a liquid crystal in a liquid crystal panel forming the liquid crystal light valve, and a polarizing plate and the like mounted on a surface of the liquid crystal panel increase the temperature for themselves by absorbing the light as well. The conventional liquid crystal projector 1 flows air around the liquid crystal light valve section 4 to maintain temperatures of these liquid crystal, the polarizing plate and the like within a predetermined specification temperature, for example, approximately 60 degrees. An intake fan 10 and an exhaust fan 12 are provided on the body, as illustrated, for performing a forced air cooling to make a air flow around the liquid crystal light valve section 4 by rotating these fans 10 and 12. Further, a filter 14 is mounted on the air inflow side of the intake fan 10 to prevent an entry of dusts and the like.
Also, a temperature detecting device 30 is mounted on the liquid crystal light valve section 4 to measure temperatures of the liquid crystal panel and the polarizing plate. A detecting signal from the temperature detecting device 30 is output to the control circuit 8 via a signal line 16. The control circuit 8 compares the temperature detecting signal from the temperature detecting device 30 with a previously memorized reference value, thereby disconnecting the lamp 2 via a signal line 20 and the power supply 26 of the liquid crystal projector 1 via a signal line 22, when the temperature detecting signal exceeds the reference value. Here, the reference value of the temperature memorized in the control circuit 8 is described with reference to FIG. 16. A lateral axis in FIG. 16 shows a room temperature (xc2x0 C.), while a vertical axis shows a temperature (xc2x0 C.) detected based on the temperature detecting signal from the temperature detecting device 30. As shown in FIG. 16, it its understood that a temperature in the liquid crystal light valve 4 increases along with an increase in room temperature in spite of the enforced air cooling by the fans 10 and 12. Therefore, in the past, the reference value as an allowable temperature for the liquid crystal and the polarizing plate is adjusted to the specification temperature to protect the inner parts of the liquid crystal light valve. So, when the temperature in the liquid crystal light valve exceeds this reference value, the power supply 26 and the lamp 2 are disconnected.
Thus, the conventional liquid crystal projector 1 measures the temperature in the vicinity of the liquid crystal panel by means of the temperature detecting device 30 arranged at the liquid crystal light valve section 4 not to give a degradation or a malfunction to the liquid crystal or the polarizing plate by the heat or light from the lamp 2, thereby disconnecting the power supply 26 and the lamp 2 by comparing the previously memorized reference value with the measurement result.
Now, as shown in FIG. 16, though the temperature in the liquid crystal projector 1 varies depending on a temperature in atmosphere wherein the liquid crystal projector 1 is arranged, the temperature in the liquid crystal projector 1 also varies from other causes, such as the extent of clogging of the filter 14 in front of the intake fan 10. In short, some causes exist until the measurement result of the temperature detecting device 30 reached the above reference value. However, under a temperature control of the above-mentioned conventional liquid crystal projector, only if the temperature of the inner parts in the liquid crystal light valve section 4 exceeds the reference value or not is judged, thus preventing the temperature variation on the way to reach the reference temperature from being grasped. Therefore, it has a problem that it is difficult to find out the causes at the time of disconnection of the power supply 26 or the lamp 2 of the liquid crystal projector from the side of users.
Also, the conventional liquid crystal projector 1 has another problem that maintenance for easily discovering preventing the efficiency deterioration of the intake fan 10 caused by the clogging of the filter 14, which is one of the causes by which the temperature of the inner parts in the liquid crystal light valve section 4 exceeds the reference temperature, is difficult.
The conventional liquid crystal projector 1 has a further problem that image quality degrades. Because even if a predetermined voltage is applied to the liquid crystal to gain a predetermined gradation in a half tone display, when the temperature of the liquid crystal panel in the liquid crystal light valve section 4 changes, transmissibity of the liquid crystal panel changes depending on it, so that the reproducibility of the half tone differs depending on the temperature.
An object of the present invention is to provide a projector type display which can be easily maintained on the user side.
Above objects are achieved by a projection type display having a light valve for modulating and emitting an incident light from a light source, a projection lens for enlarging and projecting the emitted light form the light valve, and a body at least containing the light valve. The projection type display comprises temperature measurement unit for measuring at least a temperature in the vicinity of the light valve and an external temperature of the body and a control system to control at least on/off of a power supply of the light source based on a temperature measured by the temperature measurement unit.
One of the aspects in the projection type display of the present invention, the temperature measurement unit at least comprises a first temperature detecting device to measure the temperature in the vicinity of the light valve and a second temperature detecting device to measure the external temperature in the vicinity of the body.
In addition, the projection type display comprises an intake fan for injecting air into the body, and the second temperature detecting device is arranged in the vicinity of the intake fan.
Further, the projection type display provides a filter on an outside air intake side of the intake fun, and the second temperature detecting device measures a temperature in the vicinity of the filter.
Furthermore, in the projection type display of the present invention, the control system comprises an estimation processing section which measures a temperature difference between the temperature in the vicinity of the light valve and the external temperature in the vicinity of the body based on measurement results of the first temperature detecting device and the second temperature detecting device, and presumes the extent of the dirt of the filter based on the temperature difference. According to the present invention, the user side can easily discover the clogging of the filter, so that an easy maintenance can be realized.
In the projection type display described above, the control system comprises a memory section to memorize a temperature measured by the temperature measurement unit immediately before a disconnection of the power supply. According to the present invention, since not only the internal temperature of the body but also the external temperature of the body are measured and memorized, the cause of the power disconnection is easily judged whether it is due to the increase in external temperature of the display or due to the malfunction of fan stop or reduction of the rotating speed, thus making it easy to analyze the causes at the time of the trouble occurrence.
Also, the control system comprises an on-screen display control circuit, and supplies a modulation signal overlapping a predetermined image on a picture signal to the light valve. Because the present invention comprised such a structure, various information can be displayed overlapping on the screen on which the picture is projected. Particularly, because the time of filter cleaning and filter change can be displayed, an easy maintenance by the user can be realized.
Further, above objects are achieved by the projection type display having a light valve for modifying and emitting an incident light from a light source, a projection lens for enlarging and projecting an emitted light from the light valve, and a body at least containing the light valve. The projection type display comprises temperature measurement unit for measuring at least a temperature in the vicinity of the light valve and a control system for shifting a level of a modulating signal input to the light valve based on the temperature measured by the temperature measurement unit. According to the structure of the projection type display of present invention, even if the gradation of the picture by the light emitted from the light valve is under the situation to receive the influence of the internal temperature of the body, the level of the modulation signal can be shifted in response to the temperature change, thus being capable for projecting a picture in high quality which prevents the deterioration in image quality.
Further, in the projection type display, the light valve comprises a liquid crystal panel which modulates the incident light by a picture signal and emits the modulated light.